1. Field of the Invention
The present invention relates to a broadband wireless access communication system, and more particularly to an apparatus and a method for controlling the operational states of a medium access control layer.
2. Description of the Related Art
A 4th generation (‘4G’) communication system, which is a next generation communication system, is being actively designed and studied in order to provide users with services having various Qualities of Service (‘QoS’) at a high transmission rate. Meanwhile, a wireless local area network (‘LAN’) system and a wireless metropolitan area network (‘MAN’) system generally provide transmission speeds of about 20 Mbps to 50 Mbps. Therefore, the current 4G communication system is developing into a system that assures mobility and a QoS in the wireless LAN and MAN systems which inturn assure a relatively-high transmission speed.
In the following description, the broadband wireless access communication system will be explained with reference to FIG. 1.
FIG. 1 is a view showing a construction of a general broadband wireless access communication system.
Prior to the explanation of FIG. 1, it is noted that a wireless MAN system is a type of broadband wireless access communication system capable of providing a wider service coverage area and a higher transmission speed than that of a wireless LAN system. An IEEE (Institute of Electrical and Electronics Engineers) 802.16a communication system applies an orthogonal frequency division multiplexing (OFDM) scheme and an orthogonal frequency division multiplexing access (OFDMA) scheme to a physical channel of the wireless MAN system in order to support a broadband transmission network. Since the IEEE 802.16a communication system applies the OFDM/OFDMA scheme to the wireless MAM system, the IEEE 802.16a communication system transmits a physical channel signal by using a plurality of sub-carriers, so that it is possible to transmit high-speed data. Meanwhile, an IEEE 802.16e communication system is achieved by supplementing the above-described IEEE 802.16a communication system to enable the mobility of an access terminal (AT). However, currently, the IEEE 802.16e communication system has not been standardized in detail.
Both IEEE 802.16a and IEEE 802.16e communication systems are broadband wireless access communication systems using the OFDM/OFDMA scheme. For the convenience of explanation, only the IEEE 802.16a communication system will be described below as an example. The IEEE 802.16a and IEEE 802.16e communication systems can use either the OFDM/OFDMA scheme or a single carrier (SC) scheme, but the following description will be given in consideration of only the OFDM/OFDMA scheme.
Referring to FIG. 1, the IEEE 802.16a communication system has a single cell structure and includes an access point (AP) 100 and a plurality of access terminals 110, 120, and 130 which are managed by the access point 100. The access point conducts signal communications with the access terminals 110, 120, and 130 by using the OFDM/OFDMA scheme.
The wireless MAN system is suitable for high-speed communication services because it has a wide service coverage area and provides a high transmission speed. However, since the wireless MAN system does not take into consideration the user's mobility, that is the mobility of an access terminal, handoff according to high-speed mobility of the access terminal is also not taken into consideration in the wireless MAN system. It is therefore necessary to develop a definite operation scheme of a medium access control (‘MAC’) layer which minimize power consumption of an access terminal moving at a high speed and supports an operation for a high-speed packet data transmission between the access terminal and an access point.